The pen name I'm showing on this account is: Nightmare Senshi.
I'm not showing multiple accounts associated with this email address, so that's not the issue. Did you clear the cache and cookies? Any old AFF cookies will cause the activation to fail.
If your password is already over 8 characters, then do NOT request a password reset. Use your current password.
When you proceed to the activation, using the link DemonGoddess provided above, the system will send you a validation email. You must click on the link in that email to proceed. If the email is not in your Inbox, check your Spam or Junk folders.